This invention relates to thermoplastic compositions, in particular filled polyester compositions, their method of manufacture, and uses of the compositions.
Molded articles comprising thermoplastic polymers are useful in the manufacture of optical reflectors, for example in automotive headlight extensions, bezels and reflectors, for indoor illumination, for vehicle interior illumination and the like. To provide adequate reflection, a surface of the molded article is coated with a reflective layer, typically a vapor deposited film of metal.
Polyesters are often used for such molded items because of their high thermal and flow properties. However, because the surfaces of the molded articles do not ordinarily possess satisfactory gloss or have some roughness, the surface is treated with a primer as an undercoat before vapor deposition of the reflective surface. Such primer treatment adds a processing cost, so improvements are sought so that vapor deposition can be performed directly on the molded item.
Surface roughness often arises from the inclusion of fillers in the polyester compositions. Fillers can impart dimensional stability to the molded articles, and in particular can decrease shrinkage of the article upon cooling in the mold. It is, therefore, desirable to develop polyester compositions that can be formed into molded items that have extremely high gloss, no surface defects visual to the eye, and low shrinkage. It would be an additional advantage if other advantageous properties of polyester compositions could be obtained, for example low out-gassing on heat treatment (which can cloud the metallized surface), and clean de-molding. It would be a further advantage if the compositions could be used in the manufacture of articles having an excellent appearance after metallization without a separate undercoating operation.